<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>CSS 层叠</title>
    <style>
      body #header .title {
        color: aquamarine;
      }
      #header .nav-link.active {
        color: red;
      }
    </style>
  </head>
  <body>
    <div id="header">
      <span class="title nav-link active">我是红色还是绿色</span>
    </div>
  </body>
</html>
